Intervertebral implant for the lumbrosacral articulation

ABSTRACT

The invention provides an intervertebral implant for the lumbo-sacral joint, the implant consisting in a spacer suitable for being placed between the fifth lumbar vertebra and the sacral vertebra articulated thereto, the body of said spacer presenting in its top face a groove extending in the midplane of the spacer and suitable for receiving the spinous process of said lumbar vertebra. A longitudinal housing oriented orthogonally to said groove is formed in the bottom face and is suitable for receiving the top portion of the sacral vertebra. The longitudinal housing is defined by an extension and by a tab of width narrower than the width of the body of the spacer. The section of the housing in the midplane of the space is generally U-shaped, being inclined relative to the bottom of the groove.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/568,307, which is a 371 Application of PCT Patent Application No.PCT/FR04/02160, filed Aug. 19, 2004, which claims priority to FrenchApplication No. 0310063, filed Aug. 21, 2003, which are hereinincorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an intervertebral implant for thelumbo-sacral joint.

BACKGROUND

In the anatomy of the spine, the sacrum, situated beneath the lumbarvertebrae, is constituted by five vertebrae which, over the course ofhuman evolution, have become fused together. The top vertebra of thesacrum, written S1, is articulated to the fifth lumbar vertebra, writtenL5. This articulated connection constitutes the lumbo-sacral joint, orthe L5-S1 joint, and is shown in FIG. 1.

Each lumbar vertebra presents a middle and posterior projection: thespinous process, sometimes referred to below as the process 10. Thesacral vertebrae have lost their spinous processes during evolution, andinstead they retain a small residual bulge 12.

In man, certain kinds of back pain can be due to stresses associatedwith relative movements between two vertebrae acting on theintervertebral disk situated between those vertebrae.

Numerous intervertebral implants are already known that seek to limitthe movements of two vertebrae relative to each other so as to relievethe intervertebral disk, and in particular the implant described indocument FR 2 775 183. That implant is a spacer presenting twolongitudinal notches on its top and bottom faces extending in the samedirection, that of the midplane of the spacer, for the purpose ofreceiving the spinous processes of the adjacent vertebrae between whichthe spacer is to be implanted. The spacer is then held in position bystraps surrounding said processes. By blocking a portion of the spine,the spacer transfers loads from above and below the vertebrae concerned,thereby relieving the intervertebral disk situated between thesevertebrae. Unfortunately, because of the anatomy of the sacral region,and more particularly because of the lack of a spinous process onvertebra S1, it is not possible to put that type of spacer into placeover the L5-S1 joint.

A type of implant described in document EP 1 13 8 2 68 is also knownthat is specifically adapted for the anatomy of the lumbo-sacral region.That implant comprises an intervertebral spacer and a link bar. Theintervertebral spacer presents two notches that are substantiallymutually orthogonal, and the link bar is secured to the sacrum by meansof two hooks secured to the vertebra S1. More precisely, the hooks bearagainst the top portion of the vertebra S1, also known as the posteriorarc, and each of them is secured to the sacrum by fastener means such asstaples that enable the hooks to be put into position and stabilized.Once the hooks are installed on the sacrum, the bar is secured to thehooks and the intervertebral spacer is put into place. The top notch inthe spacer is suitable for receiving the spinous process on vertebra L5,while the bottom notch is of a shape that is suitable for receiving thebar, such that the spacer rests on the bar.

Nevertheless, that type of implant suffers from numerous drawbacks.Firstly, in the short term, fastening hooks to the sacrum, e.g. bystaples, can be traumatic for the patient. Subsequently, in the mediumto long term, the compression and extension stresses to which theimplant is subjected are transferred to the means for fastening thehooks to the sacrum and lead to the holes in which the fastener meansare secured becoming larger. Play is then created between the sacrum andthe hooks, which can lead to the implant having poor mechanicalbehavior, or even to the fastener means being torn loose. The traumasuffered by the patient is then major, and a new operation must beenvisaged in order to withdraw and possibly replace the defectiveimplant.

The present invention seeks to solve the drawbacks of existing devices.

SUMMARY

To this end, the invention provides an intervertebral implant for thelumbo-sacral joint, the implant consisting of a spacer suitable forbeing placed between the fifth lumbar vertebra L5 and the vertebra S1 ofthe sacrum that is articulated thereto. The body of said spacer presentstwo opposite end faces, a top face and a bottom face. The spacerpresents a groove extending along the midplane of the spacer and formedin the top end face and suitable for receiving the spinous process ofsaid lumbar vertebra L5. The spacer also presents a longitudinal housingextending orthogonally to said groove and formed in the bottom end face,being suitable for receiving the top portion of the sacral vertebra S1,such that the spacer rests directly on said top portion.

The implant thus comprises no more than an intervertebral spacer, andthe spacer can be put into direct contact with the sacral vertebra S1without it being necessary to use other elements such as a fastener bar,thus making it easier to put into place.

In a first aspect of the invention, the body of said spacer presentsfirst and second opposite side faces into which said groove opens out,and presents at its bottom end an extension having a first sideextending the first side face, and a second side that is opposite fromits first side and that defines a setback relative to the second sideface of the body of the spacer, the spacer also including a tab of widthnarrower than the width of the body of the spacer in the directionorthogonal to the midplane of the spacer, connected to the body of thespacer, and extending facing the second side of said extension in such amanner that the inside face of said tab facing the second side of theextension co-operates with said second side to define the outline ofsaid housing.

The small width of the tab enables the implant to adapt better to theanatomy of the sacral region. The top portion of the sacral vertebra S1forms a posterior arc. This posterior arc is concave and co-operateswith the anterior portion of the sacrum, known as the vertebral body, todefine an orifice through which the spinal cord passes: the vertebralforamen. The invention seeks to limit the space occupied by the tabinside said orifice so as to leave as much space as possible availablefor the spinal cord, and thus avoid subjecting it to stresses thatgenerally lead to pain for the patient.

For this purpose, the width of the tab is sufficiently narrow relativeto that of the body of the spacer to enable it to engage deeply in thecavity formed by the posterior arc. Nevertheless, the dimensions of thetab cannot be made so small as to run the risk of it breaking under theeffect of the stresses to which it is subjected. The width selectedshould therefore take account of the mechanical properties of thematerial used for making said tab.

It should be observed that the surface of the body of the spacersituated at the bottom of the housing, i.e. at the base of the tab,constitutes the surface whereby the spacer bears against the top edge ofthe posterior arc of the sacrum, and that the body of the spacer at thislevel must therefore be of a width that is sufficient to provide stablesupport.

Advantageously, the inside face of said tab situated facing the setbackcan be convex in such a manner as to present a shape that iscomplementary to the shape of the inside face of the posterior arc,facing towards the vertebral body. This characteristic enables the tabto fit closely to the shape of this wall and thus to occupy a limitedamount of space inside the vertebral foramen.

According to a second aspect of the invention, the section in themidplane of the spacer of the housing formed in the bottom end face andsuitable for receiving the top portion of vertebra S1, is generallyU-shaped, and the midplane of this housing is not orthogonal to themidplane defined by the bottom of said groove.

The particular inclination and shape of the housing seek to improve thesupport of the spacer on the posterior arc of vertebra S1, which is notorthogonal to the portion of the spinous process of vertebra L5 that isto come into contact with the bottom of the groove, and having a topedge that presents a convex shape. These characteristics also make iteasier to put the space into place.

Advantageously, the midplane of said housing is inclined relative to themidplane defined by the bottom of said groove at an angle lying in therange 40° to 80°. This inclination guarantees that the spacer is stablewhen it is in place.

Since the outline of the housing is defined by the inside face of thetab and the second side of said extension, the midplane of the housingextends relative to the midplane defined by the bottom of the groove ina manner that depends on the general inclination of the inside face ofthe tab and of the second side of the extension.

Thus, advantageously, a zone of the inside face of the tab slopesrelative to the midplane defined by the bottom of said groove at anangle A lying in the range 60° to 80°, and preferably substantiallyequal to 70°, and a portion of the second side of the extension isinclined relative to the midplane defined by the bottom of said grooveat an angle B lying in the range 40° to 70°, and preferably in the range50° to 60°.

In another particular embodiment of the invention, a notch is formed insaid extension facing said tab. The bulge situated on the posterior faceof the sacrum, constituting the residual trace of a spinous processbeing present on sacral vertebra S1, is thus received within said notchwhen the implant is put into place, thus enabling the stability of theimplant to be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages can be better understood on reading thefollowing detailed description of two embodiments of the invention shownin the accompanying figures.

FIG. 1 is a diagram showing the anatomy of the lumbo-sacral region ofthe spine.

FIG. 2 shows a first embodiment of the implant of the invention put intoplace between lumbar vertebra L5 and sacral vertebra S1.

FIGS. 3 and 4 show said first and second side faces of the body of theFIG. 2 spacer.

FIG. 5 is a section view of the body of the FIG. 2 spacer on itsmidplane M.

FIG. 6 shows a second embodiment of the implant of the invention, putinto place between lumbar vertebra L5 and sacral vertebra S1.

FIGS. 7 and 8 show said first and second side faces of the body of theFIG. 6 spacer.

FIG. 9 is a section view of the body of the FIG. 6 spacer on itsmidplane M′.

DETAILED DESCRIPTION

The fifth lumbar vertebra L.5 and the top sacral vertebra S1 are showndiagrammatically in FIG. 1. In its middle posterior portion, vertebra L5presents a spinous process 10. This process 10 is situated in thesagittal plane of the spine. The vertebra S1 does not possess a spinousprocess, and instead on its posterior face it presents a residual bulge12.

The top portion of the vertebra S1 forms a posterior arc 14. The insideface of the posterior arc faces the vertebral body 15 of the sacrum, itis concave, and it co-operates with the vertebral body to define anorifice through which there passes the spinal cord (not shown), whichorifice is known as the vertebral foramen 16.

As shown in FIGS. 2 and 6, the implant of the invention is suitable forbeing put into place between the spinous process 10 and the posteriorarc 14. It makes it possible to limit the movement of the vertebra L5relative to the vertebra S1 and thus enables the intervertebral disk 17situated between these two 5 vertebrae to be relieved of the stressesthat result from such movement.

With reference to FIGS. 2 to 5, there follows a description of a firstembodiment of the intervertebral implant of the invention.

This implant consists in a spacer 20 whose body 21 is shown in FIGS. 3to 5. The body of the spacer is made of a biocompatible material, e.g. abiopolymer. In the embodiment shown, the body 21 is molded out ofpolyetheretherketone, referred to below as PEEK. The polymer is of thetype sold in particular under the trademark PEEK®.

The body 21 of the spacer presents a top end face 22 and a bottom endface 24 opposite from the face 22. It also presents first and secondopposite side faces 26 and 28.

The midplane M of the spacer intersects the faces 22, 24, 26, and 28,and it subdivides the body 21 into two almost symmetrical portions thatdiffer from each other only by the presence in one of the portions of acavity that is suitable for receiving fastener means. When the spacer isput into place on the spine, the plane M corresponds substantially tothe sagittal plane of the spine.

A groove 30 occupying the midplane M of the spacer 20 is formed in thetop end face 22 of the body 21 and is suitable for receiving the process10 of the lumbar vertebra L5. This groove opens out into the side faces26 and 28. The section of the groove 30 in the plane perpendicular tothe midplane M of the spacer is substantially U-shaped with asubstantially plane base. This shape enables it to receive the bottomportion of the process 10.

The body 21 of the spacer 20 presents an extension 32 at its bottom end,which extension has a first side 32 b extending the first side face 26,and a second side 32 a opposite from the first side defining a setbackrelative to the second side face 28 of the body 21 of the spacer. Thespacer 20 also comprises a tab 34 connected to the body 21 of thespacer, and in the present example integrally molded therewith. The tab34 extends facing the second side 32 a of the extension 32 and it iscurved: it begins by going away from the side 32 a and from the face 26,prior to coming closer to the side 32 a.

The size of the tab 34 in the direction orthogonal to the midplane M ofthe spacer 20, i.e. the width of the tab, is less than the width of thebody 21 of the spacer. For example, the width of the tab 34 issubstantially equal to 9 millimeters (mm), whereas the width of the body21, and more particularly in the vicinity of the tab 34 in the zone thatis to bear against the posterior arc 14 of the sacrum, is substantiallyequal to 18 mm, i.e. twice the width of the tab. The mean thickness ofthe tab 34 is substantially equal to 2 mm. For a tab 34 made of PEEK,these dimensions are sufficient to enable the tab 34 to withstand thestresses to which it is subjected.

The inside face 34 a of the tab 34 facing towards the second side 32 aof the extension, co-operate with said second side to define the outsideof a longitudinal housing 36. This housing 36 formed in the bottom endface 24 extends orthogonally relative to the groove 30 and is suitablefor receiving the posterior arc 14 of the sacral vertebra S1. Thus, onceput into place, the spacer 20 rests directly on the sacrum.

In order to facilitate contact between the spacer 20 and the posteriorarc 14 of the sacrum, the section of the housing 36 in the midplane M ofthe spacer is generally U-shaped, and the midplane L of the housing 36is not orthogonal to the midplane F defined by the bottom of the groove30.

More precisely, in the example shown, the midplane L of the housing 36is inclined relative to the midplane F at an angle I lying in the range50° to 70°. This inclination depends firstly on the general inclinationof the inside face 34 a of the tab 34 relative to the plane F, andsecondly on the inclination of the second side 32 a of the extension 32relative to said plane. Thus, a zone of the inside face 34 a of the tab34 is inclined relative to the midplane F at an angle A that issubstantially equal to 70° as shown in FIG. 5, and a portion of thesecond side 32 a of the extension 32 is inclined relative to themidplane F at an angle B that is substantially equal to 50°.

As shown in FIG. 1, the spacer also presents first and second fastenermeans 42 and 44 serving to enable the body 21 of the spacer to besecured respectively to the process 10 of the lumbar vertebra L5, and tothe sacral vertebra S1.

These fastener means are similar to those described in document FR01/03362, each comprising a strap 46, 46′ and a fastener system securedto the body of the spacer.

The fastener system is formed by a plate suitable for being receivedinside a cavity of complementary shape formed in the body 21 of thespacer. The plate presents studs on two of its opposite side edgessuitable for being engaged by force into housings provided for thispurpose in the cavity of the body 21 so as to be held therein. Thisenables the plate to be secured to the body 21 of the spacer.

Each plate also presents two slots through which the straps 46, 46′ canbe passed. These slots are inclined so as to allow the straps to move inone direction only, corresponding to tightening.

Concerning the first fastener means 42, the first end on the strap 46 ispassed through an oblong opening 48 situated along a first side of thegroove 30 and passing through the body 21 of the spacer, and is thenfolded over and stitched to itself so as to form a loop. The first endof the strap 46 is thus secured to the body of the spacer 21.

The other end of the strap 46 is passed into a fastener system situatedalong the side of the groove 30 that is opposite from said first side.When the spacer is put into place, the strap 46 is tightened around theprocess 10.

The second fastener means 44, different from the first, are shown inFIGS. 2 and 5. As can be seen in FIG. 5, a hole 38 is formed in the body21 of the spacer and opens out on one side into the bottom of thehousing 36 in the vicinity of the tabs 34, and on the other side intothe bottom of the groove 30. This hole is suitable for receiving aportion of the strap 46′. In the vicinity of the groove 30, another hole40 is formed in the body 21. This hole 40 crosses the hole 38orthogonally and is smaller in diameter than the hole 38. The hole 40opens out on one side of the body of the spacer and is suitable forreceiving a pin (not shown).

The strap 46′ is slid into the hole 38 and the pin is passed into a loopformed at the first end of said strap 46′. Thus, the first end of thestrap 46′ is secured to the body 21 of the spacer by means of the pin.The other end 46′ is passed into the fastener system 44 situated on thefirst side face 26 of the body of the spacer.

As shown in FIG. 2, when the spacer is in place, the strap 46′ passesbetween the posterior arch 14 of the sacrum and the inside face 34 a ofthe tab 34, then along a portion of the vertebra S1, prior to passingthrough an opening 60 made for this purpose in the sacrum after which itrises back towards the fastener system 44.

When the body 21 of the spacer and the tab 34 are made of PEEK, and thestrap 46′ is made of woven polyester yarn, the outside face of the tabis smoother than the face of the strap. It is then advantageous sinceless trauma is involved for the spinal cord, to encourage contactbetween the tab 34 and the spinal cord and to limit contact between thestrap 46′ and the spinal cord. That is why the tab 34 covers the strap46′ when the spacer is in place.

A second embodiment of the implant of the invention is shown in FIGS. 6to 10. This implant likewise consists in a spacer 120. Since the shapeof this spacer is close to that of the first embodiment, the numericalreferences specifying the portions of the spacer 12 0 that are similarto portions of the spacer 20 correspond to the numerical references usedfor the spacer 20 plus 100.

The top portion of the body 121 of the spacer 120 is identical to thatof the body 21 of the spacer 20; the body 121 presents a groove 130 forreceiving the process of the vertebra L5, and the first fastener means142 comprise a strap 146 held by a fastener system and serving to betightened around the process 10 in such a manner as to hold it in thegroove 130.

The bottom portion of the body 121 differs from that of the body 21.Firstly, the tab 134 is longer and wider than the tab 34. The tab 134seeks to replace the fastener means 44 for fastening the spacer 20 tothe sacrum, and therefore needs to be long enough to descend along theposterior arc 14 of the vertebra S1 and to ensure that the spacer 120 isheld on said arc 14. Furthermore, since it is subjected to high levelsof stress, its length and its thickness, mainly in the vicinity of thebody 121 of the spacer must be sufficient to prevent any breakage. Thethickness of the tab 134 is compensated by the absence of the strap,such that like the first embodiment, once the spacer 120 is in place,the tab 134 occupies as little space as possible inside the vertebralforamen, so as to limit contact with the spinal cord.

The housing 136 situated in the bottom end face 124 of the spacer isdefined by the tab 134 and the extension 132. The section of thishousing 136 on the midplane M of the spacer is generally U-shaped, andthe mean plane L′ of said housing is inclined relative to the mean planeF′ defined by the bottom of the groove 130 by an angle I′ lying in therange 60° to 70°. The angles A and B represent respectively theinclination between a zone of the inside face 134 a of the tab 134 andthe mean plane F′ defined by the bottom of the groove 130, and theinclination between a portion of the second side 132 a of the extension132 and the mean plane F′, and these angles are substantially equalrespectively to 70° and 60°.

Since the spacer does not have any means for fastening it to the sacrum,the walls of the housing 136 are closer to each other than in the firstembodiment, and the angle that exists between the second side 132 a ofthe extension 132 and the inside face 134 a of the tab 134 issubstantially equal to 10°, whereas it is nearer 20° in the firstembodiment. Thereafter, the bottom of the housing 136 presents a concaveshape that is more marked in order to receive more closely the top edgeof the vertebra S1 which is convex.

Furthermore, as shown in FIGS. 6, 7, and 9, a notch 150 is formed in theextension 132 facing the tab 134 so that when the spacer is being putinto place, the residual bulge 12 situated on the posterior face of thevertebra S1 is received in the notch 150, thus improving the stabilityof the spacer 120 on the sacrum. The bottom 150 a of the notch 150 maybe substantially parallel to the mean plane F¹, or it may be inclinedrelative to said plane at an angle that is substantially equal to 20°,as shown in FIG. 9.

The spacer 120 also presents a hole 152 parallel to the plane F′ definedby the bottom of the groove 130 and situated beneath said groove,passing through the body 121 of the spacer 120. This hole opens out intothe first and second side faces 126 and 128 of the body of the spacer120, and is provided to pass an instrument that is used for holding thespacer 120 while it is being put into place.

1. A method of limiting the displacement of the fifth lumbar vertebrarelative to the sacral vertebra of a spinal column, the fifth lumbarvertebra including a spinous process and the sacral vertebra including avertebral foramen defined between a posterior arc of the sacral vertebraand a vertebral body of the sacral vertebra, the method comprising:inserting a spacer of an intervertebral implant between the fifth lumbarvertebra and the sacral vertebra such that the spinous process of thefifth lumbar vertebra is received in a groove of the spacer and restsdirectly against the spacer and the posterior arc of the sacral vertebrais received in a longitudinal housing of the spacer and rests directlyagainst the spacer.
 2. The method of claim 1, wherein the longitudinalhousing is defined between a surface of an extension of the spacer and asurface of a tab spaced from the extension.
 3. The method of claim 2,wherein the housing extends generally orthogonal to the groove.
 4. Themethod of claim 2, wherein the tab of the spacer is inserted into thevertebral foramen of the sacral vertebra between the posterior arc ofthe sacral vertebra and the vertebral body of the sacral vertebra.
 5. Amethod of limiting the displacement of the fifth lumbar vertebrarelative to the sacral vertebra of a spinal column, the methodcomprising: providing an intervertebral implant comprising: a spacerhaving a superior end, an inferior end opposite the superior end, ananterior face, and a posterior face opposite the anterior face; thesuperior end of the spacer including a groove defined between a firstside surface and a second side surface, wherein the groove is adapted toreceive a spinous process of the fifth lumbar vertebra between the firstside surface and the second side surface, the groove extending throughthe spacer from the anterior face to the posterior face; the inferiorend of the spacer including an extension having a first side and asecond side, and a tab spaced from the extension, wherein a housingextending generally orthogonal to the groove is defined between thesecond side of the extension and a side face of the tab facing theextension, wherein the housing is adapted to receive a top portion ofthe sacral vertebra between the second side of the extension and theside face of the tab; and inserting the intervertebral implant betweenthe fifth lumbar vertebra and the sacral vertebra such that the spinousprocess of the fifth lumbar vertebra is received in the groove of thespacer and rests directly against the spacer and the top portion of thesacral vertebra is received in the longitudinal housing of the spacerand rests directly against the spacer.
 6. The method of claim 5, whereinthe tab of the spacer is inserted into a vertebral foramen of the sacralvertebra defined between a posterior arc of the sacral vertebra and avertebral body of the sacral vertebra.
 7. The method of claim 5, furthercomprising: securing the spinous process of the fifth vertebra in thegroove by tightening a strap of the intervertebral implant against thespinous process.
 8. The method of claim 5 further comprising: securingthe top portion of the sacral vertebra in the housing by tightening astrap of the intervertebral implant against the sacral vertebra.
 9. Themethod of claim 8, further comprising: forming an opening through thesacral vertebra; and passing the strap through the opening of the sacralvertebra.
 10. The method of claim 5, wherein the spacer includes amidplane which intersects each of the superior end, the inferior end,the anterior face and the posterior face of the spacer, the midplanebisecting the groove.
 11. The method of claim 10, wherein the tab has awidth measured in a direction orthogonal to the midplane of the spacerwhich is less than a width of the extension measured in a directionorthogonal to the midplane of the spacer.
 12. The method of claim 5,wherein a first portion of the tab curves away from the extension and asecond portion of the tab curves toward the extension.
 13. The method ofclaim 5, wherein the side face of the tab is convex.
 14. The method ofclaim 5, wherein a notch formed in the extension receives a residualbulge on the sacral vertebra.